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SubjectRe: [RFC PATCH 02/35] vfs: add path_open()
On Thu, Apr 12, 2018 at 05:07:53PM +0200, Miklos Szeredi wrote:
> Currently opening an overlay file results in:
>
> - the real file on the underlying layer being opened
> - f_path being set to the overlay {mount, dentry} pair
>
> This patch adds a new helper that allows the above to be explicitly
> performed. I.e. it's the same as dentry_open(), except the underlying
> inode to open is given as a separate argument.
>
> This is in preparation for stacking I/O operations on overlay files.
>
> Later, when implicit opening is removed, dentry_open() can be implemented
> by just calling path_open().
>
> Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
> ---
> fs/open.c | 27 +++++++++++++++++++++++++++
> include/linux/fs.h | 2 ++
> 2 files changed, 29 insertions(+)
>
> diff --git a/fs/open.c b/fs/open.c
> index 7ea118471dce..8c315f9ec2f6 100644
> --- a/fs/open.c
> +++ b/fs/open.c
> @@ -866,6 +866,33 @@ int vfs_open(const struct path *path, struct file *file,
> return do_dentry_open(file, d_backing_inode(dentry), NULL, cred);
> }
>

This really warrants some kernel-doc. Let me try to get this started and
you can fix it:

/**
* path_open() - Open an inode by a particular name.
* @path: The name of the file.
* @flags: The O_ flags used to open this file.
* @inode: The inode to open.
* @cred: The task's credentials used when opening this file.
*
* ...
*
* Context: Process context.
* Return: A pointer to a struct file or an IS_ERR pointer. Cannot return NULL.
*/

> +struct file *path_open(const struct path *path, int flags, struct inode *inode,
> + const struct cred *cred)
> +{
> + struct file *file;
> + int retval;
> +
> + file = get_empty_filp();
> + if (!IS_ERR(file)) {
> + file->f_flags = flags;
> + file->f_path = *path;
> + retval = do_dentry_open(file, inode, NULL, cred);
> + if (retval) {
> + put_filp(file);
> + file = ERR_PTR(retval);
> + } else {
> + retval = open_check_o_direct(file);
> + if (retval) {
> + fput(file);
> + file = ERR_PTR(retval);
> + }
> + }
> + }
> +
> + return file;

I'd find this clearer written like this ...

+ file = get_empty_filp();
+ if (IS_ERR(file))
+ return file;
+
+ file->f_flags = flags;
+ file->f_path = *path;
+ retval = do_dentry_open(file, inode, NULL, cred);
+ if (retval)
+ goto err;
+ retval = open_check_o_direct(file);
+ if (retval)
+ goto err;
+ return file;
+err:
+ put_filp(file);
+ return ERR_PTR(retval);

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